X-ray tube apparatus

ABSTRACT

Conventionally, the magnetic field generator was arranged perpendicularly to the axis of the electron beam. The magnetic field generator of this invention is arranged so as to be inclined relative to the plane perpendicular to the axis of the electron beam. Specifically, the magnetic field generator is arranged so as to be inclined relative to the plane perpendicular to the axis of the electron beam within the range in the cathode side from the focused and deflected electron beam. Inclination up to the anode side opposite to the cathode side will lead to a possibility of increasing the reduced X-ray source diameter. Thus, arranging the magnetic field generator so as to be inclined within the range in the cathode side from the electron beam may reduce the X-ray source diameter.

TECHNICAL FIELD

This invention relates to an X-ray tube apparatus. More particularly,this invention is directed to an X-ray tube, such as an X-ray tube of asystem that an anode rotates together with an enclosure, in which anelectron beam is focused and deflected by a magnetic field generator,typified by a quadrupole magnetic field lens etc., to collide against atarget.

BACKGROUND ART

Conventional X-ray tube apparatus include an enclosure rotation typeX-ray tube apparatus in which an anode rotates together with anenclosure, and an electron beam from an electron source of a cathodeprovided about an axis in the X-ray tube is focused and deflected by amagnetic field generator provided out of the X-ray tube to form a focalspot in a predetermined position on a target disk of the anode (see, forexample, patent document 1). The magnetic field generator of this typeprovided in the enclosure rotation type X-ray tube apparatus is formedof a coil and yoke. The generator generates a focusing magnetic fieldfor focusing an electron beam, and may also generate a deflectionmagnetic field superimposed thereon for deflecting the electron beam.Such magnetic field generators include, for instance, a quadrupolemagnetic field lens and an octupole magnetic field lens. Accordingly,the electron beam may be focused and deflected to form a focal spot in apredetermined position on the target disk of the anode. Moreover,rotation of the anode will avoid concentrated collision of the focusedand deflected electron beam in a same position on the target disk.Consequently, heat generated due to collision of the electron beam willnot be concentrated in the same position on the target disk, leading toprevention of the target disk from being molten. Furthermore, the heatgenerated due to the collision of the electron beam is dissipated fromthe target integrated into the enclosure out of the X-ray tube throughheat conduction, which may realize an improved cooling efficiency in theX-ray tube and successive irradiation with X-rays without any necessityof a cooling time.

-   [Patent Document 1]-   U.S. Pat. No. 5,883,936

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

However, the X-ray tube apparatus of this type has a problem that, sincethe focal spot is formed in the predetermined position on the target bydeflecting the electron beam, a diameter of the spot colliding againstthe anode (focal spot size), i.e., an X-ray source diameter, cannot bereduced.

This invention has been made regarding the state of the art noted above,and its object is to provide an X-ray tube apparatus capable of reducingan X-ray source diameter.

Means for Solving the Problem

To fulfill the above object, Inventors have made intensive research andattained the following findings.

That is, even though operation is performed to control conditions of theelectron beam, such as magnetomotive force given by a product of currentfed through the magnetic field generator and a number of turns of a coilor voltages applied to the cathode and the anode, there is a limit toreduction of the X-ray source diameter. Then, an idea on operatingcontrol conditions of the electron beam has been changed, and anattention is given to modifying of a structure itself of the X-ray tubeapparatus. For instance, the magnetic field generator, which is parallelto a plane perpendicular to an axis of the electron beam, i.e.,perpendicular to the axis of the electron beam, is made so as to beinclined relative to the plane perpendicular to the axis of the electronbeam. FIG. 2( a) is a graph of variations in an inclination angle andthe focal spot size in accordance with it. FIG. 2( b) is a simulationresult of the focal spot size where the magnetic field generator was notinclined. FIG. 2( c) is a simulation result of the focal spot size wherethe magnetic field generator was inclined. Herein, the focal spot sizevaries under various conditions. Thus, it should be noted that the focalspot size of FIG. 2 is data for reference.

As is also apparent from FIG. 2( b), where the magnetic field generatorwas not inclined, the focal spot size had a length in a transversedirection L₁ of 0.59 mm and a width in a longitudinal direction L₂ of0.71 mm. On the other hand, as is apparent from FIG. 2( c), where themagnetic field generator was inclined at 25 degrees relative to theplane perpendicular to the axis of the electron beam, the focal spotsize had a length in a transverse direction L₁ of 0.48 mm and a width ina longitudinal direction L₂ of 0.39 mm. Particularly, the width in thelongitudinal direction L₂ where the magnetic field generator wasinclined at 25 degrees may be reduced in size to be around half thewidth in the longitudinal direction where the magnetic field generatorwas not inclined. From this, it may be assumed that inclination relativeto the plane perpendicular to the axis of the electron beam leads to areduced width in a projection direction, i.e., the width in thelongitudinal direction L₂. As illustrated in FIG. 2( a), it is actuallyconfirmed that when the inclination angle varies, the focal spot size(in the width in the longitudinal direction L₂) becomes smaller as theinclination angle becomes larger. Consequently, from the results of FIG.2, the finding has been obtained that the X-ray source diameter may bereduced by arranging the magnetic field generator so as to be inclinedrelative to the plane perpendicular to the axis of the electron beam.

This invention based on the above finding adopts the followingconfiguration. An X-ray tube apparatus of this invention is an X-raytube apparatus to generate X-rays, including a cathode to generate anelectron beam, a magnetic field generator to generate a magnetic fieldfor focusing and deflecting the electron beam from the cathode, an anodeto generate X-rays upon collision of the electron beam focused anddeflected by the magnetic field generator, and an enclosure toaccommodate the cathode and the anode inside thereof and rotate togetherwith the anode, in which the magnetic field generator is arranged so asto be inclined relative to a plane perpendicular to an axis of theelectron beam.

According to the X-ray tube apparatus of this embodiment, the X-raysource diameter may be reduced by arranging the magnetic field generatorso as to be inclined relative to the plane perpendicular to the axis ofthe electron beam.

In the X-ray tube apparatus of the foregoing embodiment, the magneticfield generator is preferably arranged so as to be inclined relative tothe plane perpendicular to the axis of the electron beam within a rangein a cathode side from the focused and deflected electron beam.Inclination of the generator up to a side opposite to the cathode side(i.e., the anode side) will lead to a possibility of increasing thereduced X-ray source diameter. Thus, inclination is preferable withinthe cathode side. An inclination angle of the magnetic field generatoris set in accordance with the X-ray source diameter (focal spot size)required. In other words, the magnetic field generator is arranged so asto be inclined relative to the plane perpendicular to the axis of theelectron beam until a desired X-ray source diameter may be obtained. Forinstance, where the X-ray source diameter (focal spot size) of 0.4 mm isrequired, the angle of the magnetic field generator is set so as to bethe X-ray source diameter of 0.4 mm. Particularly, the magnetic fieldgenerator is preferably arranged so as to be inclined relative to theplane perpendicular to the axis of the electron beam until the X-raysource diameter is reduced by 50% compared to the magnetic fieldgenerator that is not inclined.

Moreover, an X-ray tube apparatus according to another embodiment thanabove is an X-ray tube apparatus to generate X-rays, including a cathodeto generate an electron beam, a magnetic field generator to generate amagnetic field for focusing and deflecting the electron beam from thecathode, an anode to generate X-rays upon collision of the electron beamfocused and deflected by the magnetic field generator, and an enclosureto accommodate the cathode and the anode inside thereof and rotatetogether with the anode, in which a distribution angle of a magneticpole that is formed by each of the magnetic pole of the magnetic fieldgenerator is made to be asymmetrical relative to a deflection directionof the electron beam.

According to the X-ray tube apparatus of this embodiment, the X-raysource diameter may be reduced by making the distribution angle of themagnetic pole that is formed by each magnetic pole of the magnetic fieldgenerator to be asymmetrical relative to the deflection direction of theelectron beam.

Moreover, an X-ray tube apparatus according to another embodiment thanthe above is an X-ray tube apparatus to generate X-rays, including acathode to generate an electron beam, a magnetic field generator togenerate a magnetic field for focusing and deflecting the electron beamfrom the cathode, an anode to generate X-rays upon collision of theelectron beam focused and deflected by the magnetic field generator, andan enclosure to accommodate the cathode and the anode inside thereof androtate together with the anode, in which a length of each magnetic poleof the magnetic field generator is made to be asymmetrical relative tothe deflection direction of the electron beam.

According to the X-ray tube apparatus of this embodiment, the X-raysource diameter may be reduced by making the length of each magneticpole of the magnetic field generator to be asymmetrical relative to thedeflection direction of the electron beam.

Furthermore, an X-ray tube apparatus according to another embodimentthan the above is an X-ray tube apparatus to generate X-rays, includinga cathode to generate an electron beam, a magnetic field generator togenerate a magnetic field for focusing and deflecting the electron beamfrom the cathode, an anode to generate X-rays upon collision of theelectron beam focused and deflected by the magnetic field generator, andan enclosure to accommodate the cathode and the anode inside thereof androtate together with the anode, in which magnetomotive force to excitethe magnetic pole of the magnetic field generator is set to beasymmetrical relative to the deflection direction of the electron beam.

According to the X-ray tube apparatus of this embodiment, the X-raysource diameter may be reduced by setting the magnetomotive force toexcite the magnetic poles of the magnetic field generator to beasymmetrical relative to the deflection direction of the electron beam.

Effect of the Invention

With the X-ray tube apparatus of this invention, the X-ray sourcediameter may be reduced by arranging the magnetic field generator so asto be inclined relative to the plane perpendicular to the axis of theelectron beam, by making the distribution angle of the magnetic polethat is formed by each magnetic pole of the magnetic field generatorasymmetrical relative to the deflection direction of the electron beam,by making the length of each of the magnetic pole of the magnetic fieldgenerator asymmetrical relative to the deflection direction of theelectron beam, or by setting the magnetomotive force to excite themagnetic pole of the magnetic field generator to be asymmetricalrelative to the deflection direction of the electron beam.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1( a) is a schematic side view of an X-ray tube apparatus accordingto Embodiment 1;

FIG. 1( b) is a schematic elevation view of a magnetic field generatorof the X-ray tube apparatus according to Embodiment 1;

FIG. 2( a) shows a graph of variations in an inclination angle and afocal spot size in accordance with the inclination angle;

FIG. 2( b) is a simulation result of the focal spot size where themagnetic field generator is not inclined;

FIG. 2( c) is a simulation result of the focal spot size where themagnetic field generator is inclined;

FIG. 3 is a schematic elevation view of the magnetic field generator ofthe X-ray tube apparatus according to Embodiment 2;

FIG. 4 is a schematic elevation view of the magnetic field generator ofthe X-ray tube apparatus according to one modification;

FIG. 5 is a schematic elevation view of the magnetic field generator ofthe X-ray tube apparatus according to another modification;

FIG. 6 is a schematic elevation view of the magnetic field generator ofthe X-ray tube apparatus according to another modification; and

FIG. 7 is a schematic elevation view of the magnetic field generator ofthe X-ray tube apparatus according to another modification.

DESCRIPTION OF REFERENCES

-   -   2 . . . cathode    -   4 . . . magnetic field generator    -   5 . . . anode    -   6 . . . enclosure    -   B . . . electron beam    -   O . . . axis of electron beam    -   V . . . plane perpendicular to axis of electron beam

Embodiment 1

Embodiment 1 of this invention will be described in detail hereinafterwith reference to the drawings. FIG. 1( a) is a schematic side view ofan X-ray tube apparatus according to Embodiment 1. FIG. 1( b) is aschematic elevation view of a magnetic field generator of the X-ray tubeapparatus according to Embodiment 1.

As illustrated in FIG. 1( a), an enclosure rotation type X-ray tubeapparatus 1 according to Embodiment 1 includes a cathode 2 to generatean electron beam B, a cylindrical electrode 3 with the cathode 2attached in a groove thereof, a magnetic field generator 4 to generate amagnetic field for focusing and deflecting the electron beam B from thecathode 2, an anode 5 to generate X-rays upon collision of the electronbeam B focused and deflected by the magnetic field generator 4, and anenclosure 6 to accommodate the cathode 2, the cylindrical electrode 3,and the anode 5 inside thereof, and rotate together with the anode 5.The cathode 2 corresponds to the cathode of this invention. The magneticfield generator 4 corresponds to the magnetic field generator of thisinvention. The anode 5 corresponds to the anode of this invention. Theenclosure 6 corresponds to the enclosure of this invention.

The cylindrical electrode 3 is arranged together with the cathode 2about the axis O of the electron beam B. The cathode 2 is composed of afilament, such as a filament formed from tungsten. When heated to hightemperatures, the filament emits a thermal electron to generate theelectron beam B. The cathode 2 is exemplified by a field emission typethat emits the electron beam by the tunnel effect with the electricfield, other than a thermo-electronic emission type represented by thefilament, etc. Thus, the types of cathode 2 are not particularlylimited.

As illustrated in FIG. 1( b), the magnetic field generator 4 is formedof a polygonal (octagonal in FIG. 1( b)) yoke, and coils winding arounda plurality of iron cores extending toward a center. The yoke is formedof a magnetic material such as iron.

Conventionally, the magnetic field generator 4 was arranged, asillustrated by a long dashed double-short dashed line in FIG. 1( a), soas to be parallel to a plane V perpendicular to the axis O of theelectron beam B, i.e., perpendicular to the axis O of the electron beamB. In contrast, the magnetic field generator 4 of Embodiment 1 isarranged, as illustrated in FIG. 1( a), so as to be inclined at aninclination angle θ₁ relative to the plane V perpendicular to the axisof the electron beam B. A symbol I is given to the axis of the inclinedmagnetic field generator 4.

The magnetic field generator 4 is preferably arranged so as to beinclined relative to the plane V perpendicular to the axis O of theelectron beam B within a range in a cathode 2 side from the focused anddeflected electron beam B. Inclination up to a side opposite to thecathode 2 side (i.e., the anode 5 side) will lead to a possibility ofincreasing the reduced X-ray source diameter. Thus, inclination ispreferable within the cathode 2 side. Let the angle that is formedbetween the axis O of the electron beam B and the electron beam Bfocused and deflected be denoted as an inclination angle θ₂. InEmbodiment 1, the electron beam B is focused and deflected at theinclination angle θ₂ of approximately 40 degrees. Thus, if it is assumedthat the inclination angle θ₁ satisfies θ₁=90°−θ₂ at maximum, themagnetic field generator 4 may be inclined relative to the plane Vperpendicular to the axis O of the electron beam B at the inclinationangle of 50 degrees (=90°−40°) at maximum. Consequently, the magneticfield generator 4 may be inclined within the range to the cathode 2 sidewithout being inclined up to an opposite side to the cathode 2 side byarranging the magnetic field generator 4 so as to be inclined relativeto the plane V perpendicular to the axis O of the electron beam B at anrange of 0 degree to 50 degrees.

Such angle θ₁ at which the magnetic field generator 4 is inclined may beset according to the required X-ray source diameter (focal spot size).That is, the magnetic field generator 4 is arranged so as to be inclinedrelative to the plane V perpendicular to the axis O of the electron beamB until the desired X-ray source diameter may be obtained. For instance,where the X-ray source diameter (focal spot size) of 0.4 mm is required,the angle θ₁ of the magnetic field generator 4 is set so as to be theX-ray source diameter (focal spot size) of 0.4 mm. Particularly, themagnetic field generator 4 is preferably arranged so as to be inclinedrelative to the plane V perpendicular to the axis O of the electron beamB until the X-ray source diameter is reduced by 50% compared to themagnetic field generator 4 that is not inclined. Taking FIG. 2( b) or2(c) mentioned above as an example, the width in the longitudinaldirection L₂ where the magnetic field generator 4 is inclined at 25degrees as illustrated in FIG. 2( c) may be reduced in size to be aroundhalf the width where the magnetic field generator 4 is not inclined asillustrated in FIG. 2( b).

The anode 5 is arranged inside the enclosure 6 so as to be integratedwith the enclosure 6. The anode 5 has a bevel target portion 5 a. Thefocused and deflected electron beam B accelerates towards the anode 5due to the high voltage electric field, and collides with the beveltarget portion 5 a, thereby generating X-rays. The enclosure 6 isevacuated. The enclosure 6 has a cathode side rotation axis 7 on thecathode 2 side and an anode side rotation axis 8 on the anode 5 side.The enclosure 6 rotates together with the anode 5 by rotating both therotation axes 7 and 8.

According to the X-ray tube apparatus 1 of Embodiment 1, the X-raysource diameter (focal spot size) may be reduced as illustrated in FIGS.2( a) and 2(b) by arranging the magnetic field generator 4 so as to beinclined relative to the plane V perpendicular to the axis O of theelectron beam B (in a range of 0 degree to 50 degrees in Embodiment 1).

Here, as illustrated in FIG. 1( b) in Embodiment 1, the distributionangle of the magnetic pole that is formed by each of the magnetic poleof the magnetic field generator 4 is made to be symmetrical relative tothe deflection direction of the electron beam B (corresponding to theplane V perpendicular to the axis of the electron beam B), and thelength of each magnetic pole of the magnetic field generator 4 is madeto be symmetrical relative to the deflection direction of the electronbeam B. Instead, use may be made of the magnetic field generator 4 asEmbodiment 2 mentioned below in which the distribution angle of themagnetic pole is made to be asymmetrical relative to the deflectiondirection of the electron beam B, the magnetic field generator 4 asModification (2) mentioned below in which the length of each magneticpole is made to be asymmetrical relative to the deflection direction ofthe electron beam B, or the magnetic field generator 4 in which thedistribution angle of the magnetic pole is made to be asymmetricalrelative to the deflection direction of the electron beam B as inEmbodiment 2 and the length of each magnetic pole is made to beasymmetrical relative to the deflection direction of the electron beam Bas in Modification (2). Such magnetic field generator 4 may be arrangedso as to be inclined relative to the plane V perpendicular to the axis Oof the electron beam B. In other words, Embodiment 1 may be combinedwith Embodiment 2 or Modification (2). In addition, the magnetic fieldgenerator 4 in which magnetomotive force to excite the magnetic poles ofthe magnetic field generator 4 is set to be asymmetrical relative to thedeflection direction of the electron beam B may be arranged so as to beinclined relative to the plane V perpendicular to the axis O of theelectron beam B, as in Modification (3) mentioned below.

Embodiment 2

Now, Embodiment 2 of this invention will be described in detailhereinafter with reference to the drawings. FIG. 3 is a schematicelevation view of the magnetic field generator of the X-ray tubeapparatus according to Embodiment 2.

In Embodiment 2, the distribution angle of the magnetic pole that isformed by each of the magnetic pole 4 of the magnetic field generator ismade to be asymmetrical relative to the deflection direction of theelectron beam B (i.e., the plane V perpendicular to the axis of theelectron beam B) (see “∘” and “∥” in FIG. 3). Here, in the X-ray tubeapparatus 1 of Embodiment 2 (see FIG. 1( a)), the magnetic fieldgenerator 4 may be arranged so as to be inclined at the inclinationangle θ₁ relative to the plane V perpendicular to the axis of theelectron beam B as Embodiment 1 mentioned above. Alternatively, asillustrated in the long dashed double-short dashed line in FIG. 1( a),the magnetic field generator 4 may be arranged so as to be parallel tothe plane V perpendicular to the axis O of the electron beam B, i.e.,perpendicular to the axis O of the electron beam B.

That is, in Embodiment 2, with the distribution angle of the magneticpole of the magnetic field generator 4 made to be asymmetrical relativeto the deflection direction of the electron beam B (the plane Vperpendicular to the axis of the electron beam B), the magnetic fieldgenerator 4 may be arranged so as to be inclined relative to the plane Vperpendicular to the axis O of the electron beam B, or may be arrangedso as not to be inclined but to be parallel. In addition, where themagnetic field generator 4 is arranged so as to be inclined at theinclination angle θ₁ relative to the plane V perpendicular to the axisof the electron beam B as in Embodiment 1 mentioned above, the magneticfield generator 4 as in Embodiment 2 is to be used, instead of themagnetic field generator 4 in Embodiment 1, in which the distributionangle of the magnetic pole is made to be asymmetrical in the deflectiondirection of the electron beam B. As a result, combination ofEmbodiments 1 and 2 is to be realized.

According to the X-ray tube apparatus 1 of Embodiment 2, the X-raysource diameter (focal spot size) may be reduced by making each magneticpole of the magnetic field generator 4 to be asymmetrical relative tothe deflection direction of the electron beam B.

This invention is not limited to the foregoing embodiments, but may bemodified as follows.

(1) This invention is applicable to an apparatus for industry use suchas a non-destructive inspecting apparatus, or a medical apparatus suchas an X-ray diagnostic apparatus.

(2) In the above Embodiment 1, the magnetic field generator 4 isarranged so as to be inclined relative to the plane V perpendicular tothe axis of the electron beam B. In the above Embodiment 2, thedistribution angle of the magnetic pole of the magnetic field generator4 is made to be asymmetrical in the deflection direction of the electronbeam B. As illustrated in FIG. 4, the length of each magnetic pole ofthe magnetic field generator 4 may also be made to be asymmetricalrelative to the deflection direction of the electron beam B (i.e., theplane V perpendicular to the axis of the electron beam B) (see “∘” and“∥” in FIG. 4).

As also described in Embodiment 2, the magnetic field generator 4 as inthe above Embodiment 1 may be arranged so as to be inclined at theinclination angle θ₁ relative to the plane V perpendicular to the axisof the electron beam B. Moreover, as illustrated in the long dasheddouble-short dashed line in FIG. 1( a), the magnetic field generator 4may be arranged parallel to the plane V perpendicular to the axis O ofthe electron beam B, i.e., perpendicular to the axis O of the electronbeam B. Where the magnetic field generator 4 is arranged so as to beinclined at the inclination angle θ₁ relative to the plane Vperpendicular to the axis of the electron beam B as in Embodiment 1mentioned above, the magnetic field generator 4 as in Modification (2)is to be used, instead of the magnetic field generator 4 in Embodiment1, in which the length of each magnetic pole of the magnetic fieldgenerator 4 is made to be asymmetrical relative to the deflectiondirection of the electron beam B. As a result, combination of Embodiment1 and Modification (2) is to be realized. According to the X-ray tubeapparatus 1 of Modification (2), the X-ray source diameter (focal spotsize) may be reduced by making the length of each magnetic pole of themagnetic field generator 4 to be asymmetrical relative to the deflectiondirection of the electron beam B.

(3) In the above Embodiment 1, the magnetic field generator 4 isarranged so as to be inclined relative to the plane V perpendicular tothe axis of the electron beam B. In the above Embodiment 2, thedistribution angle of the magnetic pole of the magnetic field generator4 is made to be asymmetrical relative to the deflection direction of theelectron beam B. Magnetomotive force to excite the magnetic pole of themagnetic field generator 4 may also be set so as to be asymmetricalrelative to the deflection direction of the electron beam B (i.e., theplane V perpendicular to the axis of the electron beam B). As mentionedabove, magnetomotive force is a product of the current fed through themagnetic field generator 4 and the number of turns of the coil on themagnetic pole of the magnetic field generator 4.

For example, as illustrated in FIGS. 5 and 6, the magnetic pole of themagnetic field generator 4 is separated into magnetic poles 4A and 4B into the deflection direction of the electron beam B. Let the current fedthrough the magnetic pole 4A be denoted as I_(A), and the current fedthrough the magnetic pole 4B as I_(B). As also illustrated in FIGS. 5and 6, let the number of turns of the lead wire around the iron core ofthe coil of the magnetic pole 4A be noted as n_(A), and the number ofturns of the lead wire around the iron core of the coil of the magneticpole 4B as n_(B), where assume that I_(A)n_(A)≠I_(B)n_(B). Moreover, usemay be made of the magnetic field generator 4 in which the distributionangle of the magnetic pole is asymmetrical relative to the deflectiondirection of the electron beam B, as illustrated in FIG. 5 incombination with the above Embodiment 2, to satisfyI_(A)n_(A)≠I_(B)n_(B). Furthermore, use may be made of the magneticfield generator 4 in which the length of each magnetic pole is made tobe asymmetrical relative to the deflection direction of the electronbeam B, as illustrated in FIG. 6 in combination with the aboveModification (2), to satisfy I_(A)n_(A)≠I_(B)n_(B).

As also described in Embodiment 2 and Modification (2), the magneticfield generator 4 as in the above Embodiment 1 may be arranged so as tobe inclined at the inclination angle θ₁ relative to the plane Vperpendicular to the axis of the electron beam B. Moreover, asillustrated in the long dashed double-short dashed line in FIG. 1( a),the magnetic field generator 4 may be arranged parallel to the plane Vperpendicular to the axis O of the electron beam B, i.e., perpendicularto the axis O of the electron beam B. Where the magnetic field generator4 is arranged so as to be inclined at the inclination angle θ₁ relativeto the plane V perpendicular to the axis of the electron beam B as inEmbodiment 1 mentioned above, the magnetic field generator 4 as inModification (3) is to be used in which the magnetomotive force toexcite the magnetic pole is set asymmetrical relative to the deflectiondirection of the electron beam B, instead of the magnetic fieldgenerator 4 in Embodiment 1. Thus, combination of Embodiment 1 andModification (3) is to be recognized. According to the X-ray tubeapparatus 1 of this Modification (3), the X-ray source diameter (focalspot size) may be reduced by setting the magnetomotive force to excitethe magnetic poles of the magnetic field generator 4 to be asymmetricalrelative to the deflection direction of the electron beam B.

(4) In each Embodiment and Modifications (2) and (3) mentioned above,combination of Embodiments 1 and 2, combination of Embodiment 1 andModifications (2) and (3), combination of Embodiment 2 and Modification(3), and combination of Modifications (2) and (3) has been eachdescribed. As illustrated in FIG. 7, Embodiment 2 may be combined withModification (2). That is, in the magnetic field generator 4, thedistribution angle of the magnetic pole may be made to be asymmetricalrelative to the deflection direction of the electron beam B, and thelength of each magnetic pole may be made to be asymmetrical relative tothe deflection direction of the electron beam B.

(5) In each Embodiment and Modification (2) and (3), combination of twoexamples from each Embodiment and Modifications (2) and (3) has beendescribed as one example. Combination of three or more examples may bemade such as combination of Embodiments 1 and 2 and Modification (2),combination of Embodiments 1 and 2 and Modification (3), combination ofEmbodiment 1 and Modifications (2) and (3), combination of Embodiment 2and Modifications (2) and (3), or combination of all Embodiments 1 and 2and Modifications (2) and (3).

(6) In each Embodiment mentioned above, the magnetic field generator(magnetic field generator 4) has been described that includes thepolygonal, typically octagonal iron core. The magnetic field generatoris not particularly limited in its shape, and may be circular, forexample. Moreover, the magnetic field generator is not limited inparticular, as is exemplified by the quadrupole magnetic field lens orthe octupole magnetic field lens.

1. An X-ray tube apparatus to generate X-rays, comprising a cathode togenerate an electron beam, a magnetic field generator to generate amagnetic field for focusing and deflecting the electron beam from thecathode, an anode to generate X-rays upon collision of the electron beamfocused and deflected by the magnetic field generator, and an enclosureto accommodate the cathode and the anode inside thereof and rotatetogether with the anode, wherein the magnetic field generator isarranged so as to be inclined relative to a plane perpendicular to anaxis of the electron beam.
 2. The X-ray tube apparatus according toclaim 1, wherein the magnetic field generator is arranged so as to beinclined relative to the plane perpendicular to the axis of the electronbeam within a range in a cathode side from the focused and deflectedelectron beam.
 3. The X-ray tube apparatus according to claim 2, whereinthe magnetic field generator is configured such that its inclinationrelative to the plane perpendicular to the axis of the electron beam isadjustable so that a desired X-ray source diameter may be obtained. 4.The X-ray tube apparatus according to claim 3, wherein the desired X-raysource diameter is a X-ray source diameter reduced by 50%.
 5. An X-raytube apparatus to generate X-rays, comprising a cathode to generate anelectron beam, a magnetic field generator to generate a magnetic fieldfor focusing and deflecting the electron beam from the cathode, an anodeto generate X-rays upon collision of the electron beam focused anddeflected by the magnetic field generator, and an enclosure toaccommodate the cathode and the anode inside thereof and rotate togetherwith the anode, in which a distribution angle of a magnetic pole that isformed by each of the magnetic pole of the magnetic field generator ismade to be asymmetrical relative to a deflection direction of theelectron beam.
 6. An X-ray tube apparatus to generate X-rays, comprisinga cathode to generate an electron beam, a magnetic field generator togenerate a magnetic field for focusing and deflecting the electron beamfrom the cathode, an anode to generate X-rays upon collision of theelectron beam focused and deflected by the magnetic field generator, andan enclosure to accommodate the cathode and the anode inside thereof androtate together with the anode, in which a length of each magnetic poleof the magnetic field generator is made to be asymmetrical relative tothe deflection direction of the electron beam.
 7. An X-ray tubeapparatus to generate X-rays, comprising a cathode to generate anelectron beam, a magnetic field generator to generate a magnetic fieldfor focusing and deflecting the electron beam from the cathode, an anodeto generate X-rays upon collision of the electron beam focused anddeflected by the magnetic field generator, and an enclosure toaccommodate the cathode and the anode inside thereof and rotate togetherwith the anode, in which magnetomotive force to excite the magnetic poleof the magnetic field generator is set to be asymmetrical relative tothe deflection direction of the electron beam.